The present invention relates to a pump which can repeatedly dispense a predetermined volume of liquid. More particularly, the present invention relates to a pump for more efficiently pumping highly viscous materials, such as shampoo or soap, without dripping or plugging. Such a pump is also capable of use at high temperatures without dripping.
British Patent No. 2119868A discloses a pump in which a piston reciprocates within a pump chamber to transport fluid out of a main fluid container. A suction valve located within the pump chamber allows fluid to flow from the main fluid container into the pump chamber. A discharge valve located on the interior of the piston permits fluid to flow from the pump chamber to a nozzle. A spring member is interposed between the piston and the bottom of the pump chamber to bias the piston into an upward position.
A positive pressure differential develops within the pump chamber as the piston is forced downward within the pump chamber. The positive pressure differential forces fluid in the pump chamber through the discharge valve and ultimately out the nozzle. The spring member forces the piston upward immediately following the discharge of fluid from the pump chamber. The upward travel of the piston causes a negative pressure differential to develop within the pump chamber. The negative pressure differential draws fluid from the main fluid container, through the suction valve, into the pump chamber.
However, a problem exists with the aforementioned pump in that fluid tends to accumulate within the nozzle during fluid discharge. The accumulation of fluid within the nozzle can lead to clogging and plugging so that fluid discharge is restricted or completely blocked. In addition, the discharge valve has difficulty closing fully when highly viscous fluids are pumped, which causes inefficient pump operation.
A problem also exists with the pump when high temperatures are present during storage. As temperatures rise, the pressure within the main fluid container increases. The increase in pressure within the main fluid container forces fluid through the suction valve and into the pump chamber. The unwanted influx of fluid from the main fluid container can force travel through the discharge valve and out the nozzle, causing fluid to drip and/or accumulate.
The present invention aims at solving the aforementioned drawbacks associated with prior art pumps.